In many front wheel drive automobiles currently on the market, the engine is mounted transversely in the engine compartment and is customarily supported on mounts and connected to a frame component of the automobile by means of a so-called torque strut. The torque strut functions to control angular displacement of the engine, such as when output torque increases during acceleration, and during braking, while accommodating normal engine oscillations, such as when the engine is operating at idle.
Known torque struts include an elongate member mounting at opposite ends a pair of sleeved rubber bushings for receiving a connecting bolt. While such struts have been capable of performing the aforedescribed functions, they have certain limitations. For instance, the rubber bushings at the ends of the struts are prone to deterioration due to large motions across the bushings while subjected to the heat of the engine so that, after a period of time, the bushings crack and stiffen. As a result, the struts develop a proclivity for transmitting vibrations and noises to the frame and hence into the passenger compartment, particularly during acceleration of the automobile when the strut is subjected to substantial tensile loads.
Special struts have been proposed to overcome some of the aforementioned problems. An example of such a strut may be found in U.S. Pat. No. 4,392,640. The patented strut utilizes rubber bushings having specially shaped interior cavities for providing the desired motion accommodation. U.S. Pat. No. 4,518,058 discloses a damped anti-torque strut which utilizes an hydraulic fluid displaceable axially in a chamber by means of a piston spring loaded into a central position. U.S. Pat. No. 4,377,216 discloses a fluid-filled vibration damping bushing that can be used in automotive applications.
A strut representing an improvement over the aforementioned struts is disclosed in U.S. Pat. No. 4,706,946 issued to Lord Corporation, the assignee of the present application. It incorporates friction elements to provide a friction damping action.
While the aforementioned struts and bushings may function satisfactorily for their intended purposes, there is a need for a durable and relatively low-cost torque strut which limits the transmission of engine vibrations over a broad range of engine operating conditions while being capable of readily being designed and manufactured to meet a wide variety of requirements.